Replace argument

[gUsTaV]

I have 3 consecutive lines of text that all end with a "new line character" followed by two lines that only contain a new line character.

The third line always ends with a number.

Example:
Name"\n"
Street Address"\n"
City"\t"State"\t"Zip Code"\n"
"\n"
"\n"

What kind of replace argument would I use to
replace all \n preceded by a letter with a \t
except when the \n is preceded by a number?

[Andreas]

replace

\([a-zA-Z]\)\n

by

\1\t


Btw,
in
replace all \n preceded by a letter with a \t
except when the \n is preceded by a number?
the second line is meaningless, if the \n is preceded by a letter, it cannot be preceded by a number...